As non-limiting examples, such a risky situation involves cases of reduced alertness, following drowsiness or a loss of consciousness, or falling cases. The effects of a drop of alertness are likely to have serious consequences when the person experiencing it drives a vehicle or a machine, the risk extending to the passengers of the vehicle or to the facilities and people close to the machine. Even a light fall, may potentially be a vital hazard when it affects an elderly or a disabled person. The risks involved in these situations are significantly reduced if suitable measures are completed on time. Thus, as a for instance, the driver a vehicle easily overestimates its state of alertness, to the point of getting caught by a real slumber. A simple alarm directed to his intention or to the passengers in the vehicle allows to make him aware of his drowsiness state and to foster him to stop driving. The harmful consequences of a falling, even heavy, are mitigated if assistance is provided to the person in a short time. Other comparable cases concern, for example, seizures.
In the US, 4% —approximately eleven million drivers—admit they have had an accident or near accident because they dozed off or were too tired to drive. According to data from Australia, England, Finland, and other European nations, drowsy driving triggers 10 to 30 percent of all crashes. Falls are the leading cause of death in people over 65. Every second of every day in the United States an older adult falls, making falls the number one cause of injuries and deaths from injury among older Americans. In 2014 alone, older Americans experienced 29 million falls causing seven million injuries and costing an estimated $31 billion in annual Medicare costs. Besides death cases, people who are victims of a fall usually experience a loss of autonomy and a loss of self-confidence that also have important consequences. Studies show that, in the case of an elderly person, the longer the time spent on the ground after a fall, the more serious the consequences. Alertness disorders may also cause a fall, they are the result of e.g. an extreme fatigue, or more commonly the result of drugs or alcohol consumption. Thus, in some instances, the detection of a loss of alertness and the warning of the person experiencing it or of one of his relatives, may prevent a fall.
Physiological measurements performed on groups of individuals in laboratory conditions, can statistically detect signs of reduced alertness, sleep, fall or loss of consciousness. These tests use multiple sensors that can be worn by an individual only in laboratory conditions. When the results of these experiments are used with the aim of developing a personal detection device, the detection quality usually drops, for various reasons, including:                it is difficult to integrate suitable sensory, in terms of the number of sensors and their reliability of measurement, in a wearable device;        the wearable device is unsightly, uncomfortable, too intrusive or too perceived by the individual and his relatives as a surveillance device, so that the individual does not wear it;        the detection reliability is not satisfactory, because of the reduced number of sensors and owing to the fact that it is based on statistical data not adapted to the individual itself and his way of life, and leads to the generation of false alarms, so that the person loses her confidence in the device and does not wear it anymore;        the detection is too late, as a for instance, a system detecting drowsiness by a continuous closing of the eyes, during one second or more, or by the detection of a head drop, detects in fact an advanced stage of drowsiness. If this detection, and possible actions that it triggers is of certain utility, a car launched at 80 mph (130 km/h) travels 118 feet (36 meters) in one second, what significantly reduces the effectiveness of any maneuver carried out by the driver, thus woken up in a critical situation;        the detection system usually uses cascading tests where the outcome of a first test determines the implementation of a second test, etc. . . . when reliability is poor it only gets worse from one test to the other and generates positives false or negatives false;        the autonomy of the personal system is low because of the power consumption of the many components and of the required computing power.        
The invention aims to solve the disadvantages of the prior art by offering a system based on an aesthetic sensor, autonomous and lightweight, specifically suited to its user.